From one of the stranger areas of the universe.
December 29, 2019 7:58 PM   Subscribe

Has some new gamma ray behavior in one of the faster pulsars known. And some very hard to grasp numbers.
(snip)
Pulsars are rapidly spinning, magnetized neutron stars left behind at the end of a star’s lifetime. Pulsar J0952-0607, a pulsar in a binary orbit with a very low-mass companion star, has the second-fastest known pulsar spin, rotating 707 times each second. For comparison, that’s about 70 times faster spin than the fastest helicopter rotors — and it’s an object that’s 10 km across and weighs more than the Sun!
posted by aleph (15 comments total) 12 users marked this as a favorite
 
According to my quick sleepy calculation, the surface of that pulsar is zooming around at about 15% of the speed of light!
posted by moonmilk at 10:06 PM on December 29, 2019 [3 favorites]


...it’s an object that’s 10 km across and weighs more than the Sun!

So they’re saying it’s like a toddler on a sugar high?
posted by From Bklyn at 2:02 AM on December 30, 2019 [3 favorites]


Finally! Something that RI is bigger than!
posted by GenjiandProust at 3:01 AM on December 30, 2019 [5 favorites]


I’d say that it would fit “comfortably” inside the tiny state, but I suspect it would be a very uncomfortable event, even leaving the gamma ray issues aside.
posted by GenjiandProust at 3:03 AM on December 30, 2019 [8 favorites]


15℅ light speed...I could reach Ganymede in like, a day.
posted by clavdivs at 8:11 AM on December 30, 2019


This raises the question: why Is it spinning? What imparted it with such a ridiculous amount of angular velocity?
posted by drivingmenuts at 9:05 AM on December 30, 2019


I’d say that it would fit “comfortably” inside the tiny state, but I suspect it would be a very uncomfortable event, even leaving the gamma ray issues aside.

Not without a parking permit, it wouldn’t.
posted by Huffy Puffy at 9:20 AM on December 30, 2019 [4 favorites]


I was also sleepy trying while to check moonmilk's numbers, but having woken up I'm getting ~7.4% reading the actual paper, and rabbitholing.

TFA says "10km across", implying diameter (which is where my 7.4% came from), but the paper uses 10km as the "canonical radius" (15% again). "Canonical neutron star" is a pretty common phrase on the web, with lots of pages and papers using the 1.4 solar mass in 10km radius figures (for example). The earliest citation I can find is this 1969 paper (paywalled).

Anyway, the canonical radius seems to come from calculations based on other neutron stars rather than observations of J0952−0607. Given that this pulsar is notable for its extreme rotational frequency, it might also be an outlier in radius.

Which means I don't get to say with any kind of confidence that the Lorenz factor on the surface is about 1.011, nor that a mefite on holiday there would have to adjust their watch by ~40 seconds every hour to keep to earth time. (That last number isn't counting gravitational time dilation anyway)
posted by polytope subirb enby-of-piano-dice at 9:21 AM on December 30, 2019 [2 favorites]


This raises the question: why Is it spinning? What imparted it with such a ridiculous amount of angular velocity?

Conservation of angular momentum (cue spinning figure skater image).

Most things in space are spinning, at least a little. So if you take a great big star, get it spinning slowly, then due to gravity at the end of its “life” it collapses, its moment of inertia is much lower (skater pulling arms in) and so it spins faster.
posted by Huffy Puffy at 9:24 AM on December 30, 2019 [6 favorites]


You know, I probably should have known that.

I was literally thinking: but a star ain’t got no arms ...

Must’ve been a helluvva big one before it contracted.
posted by drivingmenuts at 12:03 PM on December 30, 2019


We're talking multiple times the size of the Sun, and with a more even mass distribution than your average long-armed figure skater, all the way down to something that would fit in Rhode Island. That's a big contraction, there.
posted by Huffy Puffy at 1:17 PM on December 30, 2019 [1 favorite]


From a post in Ethan Siegal's physics and astronomy blog, Starts with a Bang :
( discussing how the extreme gravity, magnetic fields, and spinning speeds of neutron stars affect their tiny distortion from a perfect sphere. )

"While there are many ways to attempt to calculate the flattening for even the fastest neutron star, with no agreed-upon equation, even this incredible rate, where the equatorial surface moves at about 16% the speed of light, would result in a flattening of only 0.0000001%, give or take an order of magnitude or two. And this is nowhere close to escape velocity; everything on the surface of the neutron star is there to stay."

Wow, "nowhere close to escape velocity"!
posted by jjj606 at 6:38 PM on December 30, 2019 [1 favorite]


Wow, "nowhere close to escape velocity"!

Most neutron stars have an escape velocity between a third and half the speed of light.
posted by Your Childhood Pet Rock at 7:05 PM on December 30, 2019 [1 favorite]


Here's a page with some pulsar sounds and simulated sounds for example. Something this fast actually turns out to just sound like a tone.
posted by Rufous-headed Towhee heehee at 5:25 AM on January 1


Beside conservation of angular momentum the supernova that creates the pulsar could impart spin. And older pulsars that are half of a binary can be spun up by mass infallling from the other half of the binary.
posted by Mitheral at 8:11 PM on January 1 [1 favorite]


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